Date of this Version
Akinrinlola, R. J. (2018). Evaluation of bacillus strains for plant growth-promotion potentials on corn (Zea mays), wheat (Triticum aestivum), and soybean (Glycine max). Masters Thesis, University of Nebraska, United States.
Plant growth-promoting rhizobacteria (PGPR) can increase plant growth and yield by facilitating nutrient availability, hormone production, and inhibiting plant deleterious microorganisms. Twelve strains of bacillus (endospore-forming bacteria belonging to the genera Bacillus, Paenibacillus and Lysinibacillus) isolated from wheat rhizospheres were assessed for plant-growth promotion attributes in greenhouse and laboratory experiments. The objectives were to assess each strain’s potential to promote growth in corn, wheat, and soybean; and to determine whether the physiological traits expressed in vitro by the strains related to their effectiveness in promoting plant growth. Greenhouse experiments to assess growth-promotion potential were conducted by applying the strains to seed of the test crops and growing the plants in a nonsterile potting mix soil for one month. Eleven of the twelve strains increased corn growth significantly compared to controls, and four of the most efficacious strains on corn- Bacillus megaterium R181, B. safensis R173, B. simplex R180, and Paenibacillus graminis R200 - also increased the growth of soybean and wheat. These strains caused higher growth stimulation on corn than on soybean and wheat. Shoot weights were frequently increased over 200% on corn compared to the controls, whereas shoot weight stimulation by these strains on soybean and wheat did not exceed 50%. The strains were also tested in vitro for traits associated with plant growth-promotion, including antagonism against bacteria and fungi, mineral nutrient conversion, and growth hormone production. None of the strains exhibited strong antagonism against fungi in vitro and few strains inhibited other bacteria. Most strains expressed indole acetic acid production and phosphate solubilization, suggesting that these mechanisms are more prevalent. No set of traits, however, was a predictor of high growth promotion efficacy. The expression of numerous traits in vitro also was not predictive of high plant growth-promotion activity. Some strains that expressed multiple traits in vitro exhibited low growth-promotion efficacy in pot tests, whereas one strain - R200 - that tested positive for only one in vitro trait showed high efficacy. This study showed that bacillus possess high potentials to increase plant growth, but their efficacy in vivo cannot be predicted by in vitro assays.
Advisors: Gary Y. Yuen and Anthony O. Adesemoye